Method for testing stress of prestressed concrete beam under wet-heat-force coupling

Abstract

The invention relates to the technical field of concrete beam stress testing, and provides a prestressed concrete beam stress testing method under wet-heat-force coupling, which comprises the following steps: S1, arranging a stress testing device, a temperature and humidity sensor and a strain gauge; s2, acquiring data of each sensor; s3, running a wet-heat-force coupling analysis fiber beam program; and S4, performing test-analysis collaborative correction. According to the method for testing the stress of the prestressed concrete beam under the wet-heat-force coupling, stress data are directly collected based on an embedded testing device of a plane section coordination principle, non-mechanical strain interference can be eliminated, an efficient fiber beam unit analysis and calculation method is constructed, a multi-module multi-field coupling fiber beam analysis program is integrated, and the method is suitable for large-scale popularization and application. According to the method, self shrinkage, drying shrinkage, intrinsic creep, drying creep, steel bar constraint and prestress relaxation effects are effectively considered, and the purposes of accurate identification of the true stress of the prestressed concrete beam and reliable evaluation of the structural performance in a complex environment are achieved.

Description

Technical Field

[0001] This application relates to the technical field of stress testing for concrete beams, and particularly to a method for stress testing of prestressed concrete beams under wet-heat-force coupling. Background Technology

[0002] Prestressed concrete beams are common flexural members in bridges and large structures, and their service safety highly depends on the accurate understanding of internal stresses. The design and safety assessment of concrete structures are usually based on calculated stress values, while stress distribution often needs to be indirectly measured through concrete deformation or strain tests. During the forming and service process, concrete is affected by various factors such as creep, shrinkage, and temperature and humidity changes, resulting in complex time-varying effects. These time-varying deformation components superimpose each other, making the accurate acquisition of stress a challenge.

[0003] In stress testing, commonly used methods mainly include stress relief and strain measurement. Stress relief measures residual stress through local unloading, while strain measurement indirectly calculates stress using sensors such as resistance strain gauges, vibrating wire strain gauges, and fiber optic grating sensors. In addition, specialized sensors such as hydraulic flat plate stress sensors, specific types of concrete stress gauges, and intelligent embedded piezoelectric ceramic sensors have been developed for stress testing. In stress analysis, traditional analysis is mostly based on empirical models. In recent years, with the development of numerical methods, various coupled models have emerged, such as thermo-chemical-mechanical models, hydrothermal-mechanical coupled models, and micro-prestressed consolidation theory. Structural analysis often uses traditional beam theory, solid finite element methods, or fiber beam element models. Regarding test-analysis collaboration, with the development of structural health monitoring and digital twin concepts, related research attempts to combine measured multi-source monitoring data with physical coupled models, finite element analysis, and parameter inversion algorithms. Some pilot projects are also promoting the use of experimental monitoring data for model identification and online calibration.

[0004] Existing technologies have several shortcomings. In stress testing, current methods cannot effectively separate mechanical strain from temperature and humidity deformation strain. Differences in sensor characteristics, size, and concrete material properties, as well as stiffness mismatches, can lead to significant errors and deviations from the true stress values. In stress analysis, sophisticated stress analysis requires complex three-dimensional solid analysis models. Existing design-based beam-and-trunk element models fail to adequately consider the coupling relationships between temperature, moisture migration, and material damage, making it difficult to accurately reflect long-term stress evolution. Traditional empirical models deviate from actual observations, resulting in poor performance in stress evolution and performance evaluation under complex environments. Regarding the collaboration between testing and analysis, there is a lack of effective coordination mechanisms. The interface between measured data and analytical models is inconsistent, making it difficult to effectively use test results for model correction and verification, thus affecting the reliability and accuracy of structural performance evaluation. Summary of the Invention

[0005] In view of this, this application aims to propose a method for testing the stress of prestressed concrete beams under wet-heat-force coupling to solve the above-mentioned technical problems and meet the needs of stress testing of concrete beams.

[0006] To achieve the above objectives, the technical solution of this application is implemented as follows: A method for stress testing of prestressed concrete beams under wet-heat-force coupling includes the following steps: S1, Deployment of stress testing device, temperature and humidity sensor and strain gauge: Deploy embedded concrete stress testing device based on the principle of plane section coordination at key sections of prestressed concrete beam, and deploy temperature and humidity sensor and strain gauge at the same time. S2, Data Acquisition: After the concrete curing is completed, stress, temperature, humidity and strain data are collected in real time, and stress, temperature, humidity and strain-time curves are output. S3, Run the wet-thermal-mechanical coupled fiber beam analysis program: Compile a multi-field coupled fiber beam analysis program based on MATLAB, Python or C++, input the data collected in step S2 and the geometric parameters and material parameters of the beam into the multi-field coupled fiber beam analysis program, divide the beam section into several fiber layers, calculate the temperature and humidity distribution and mechanical response of each fiber layer step by step, and obtain the results such as cross-sectional stress distribution, curvature change and prestress loss; S4, Test-Analysis Collaborative Correction: Import the measured stress data into the multi-field coupled fiber beam analysis program, establish a one-to-one correspondence between test points and calculated fibers, and automatically call the parameter inversion module when the deviation between the measured stress and the calculated stress exceeds the preset threshold to correct the concrete creep coefficient, humidity diffusion coefficient, thermal expansion coefficient and damage evolution parameters, realize the dynamic calibration of the model of the multi-field coupled fiber beam analysis program, and output stress evolution curve, cross-sectional stress cloud diagram and structural performance evaluation results.

[0007] Furthermore, the stress testing device includes: Rigid sleeve; A column-type tensile and compressive stress sensor is embedded inside the rigid sleeve to form a rigid zone with the rigid sleeve for deformation coordination, thereby enabling direct measurement of internal stress in concrete. A soft gasket is fitted to the bottom of the rigid sleeve to adjust the contact position between the rigid sleeve and the concrete. A soft porous tube is inserted into the top of the rigid sleeve along the axial direction and connected to the column-type tensile and compressive sensor to form an isolation zone, separating the concrete in the test area from the concrete in the non-test area. A soft gasket ring is fitted to the top of the rigid sleeve and is used to adjust the contact position between the rigid sleeve and the concrete in conjunction with the soft gasket. The positioning rod is inserted perpendicularly to the side of the rigid sleeve and is used to define the position within the reinforcing cage or formwork.

[0008] Furthermore, step S1 includes the following sub-steps: S11, process each component of the stress testing device, install the column-type tensile and compressive sensor into the rigid sleeve and calibrate it, and then fix the other components in sequence with bolts; S12, the stress testing device is installed into the template or steel cage, and then concrete is poured simultaneously in the test area and the non-test area. After hardening, a coordinated prism is formed, and the stress value is calculated by reading the test values ​​of the tension and compression sensors. S13. According to actual needs, the stress testing device and strain gauge are respectively arranged in the mid-span area, support area and tensioning end of the prestressed concrete beam; after the arrangement is completed, zero-point calibration and sensitivity calibration are performed on all channels to ensure the consistency of signal output. Humidity sensors are embedded at the upper and lower edges of the cross section to measure humidity changes under different drying and sealing conditions; under the same environment, sealed specimens and specimens with different drying conditions are made for the calibration of concrete material performance parameters.

[0009] Furthermore, the multi-field coupled fiber beam analysis program in step S3 is pre-integrated with multiple functional modules, including: The cross-sectional humidity analysis module is based on the transient humidity diffusion control equation, taking into account the influence of temperature on the humidity diffusion coefficient, and calculates the relative humidity within the cross section. The cross-sectional temperature analysis module is based on the transient heat conduction control equation and calculates the temperature gradient distribution of each fiber layer through spatial discretization and time integration. The structural field analysis module uses the micro-prestressed consolidation MPS theory and the fiber-discrete Timoshenko beam theory to calculate the section stress, curvature and overall beam response. It also simulates concrete shrinkage and creep, steel reinforcement constraint, prestressing tendon stress relaxation and time-varying internal force redistribution.

[0010] Furthermore, the multi-field coupling equations used in the multi-field coupled fiber beam analysis program in step S3 include: The humidity field equation adopts the Fick diffusion equation, taking into account the change of boundary humidity gradient; The temperature field equation adopts the concrete heat transfer control equation, taking into account the influence of temperature changes on heat conduction. The structural field equations are established based on the constitutive model of micro-prestressed consolidation MPS theory, combined with Timoshenko beam theory and beam element fiberization analysis method.

[0011] Furthermore, step S3 includes the following sub-steps: S31, Input and Initialization: Input the data collected in step S2, as well as the beam's geometric parameters and material parameters, into the multi-field coupled fiber beam analysis program. S32, Temperature and humidity field calculation and fiber division: The beam section is divided into several fiber layers according to the temperature and humidity distribution law of the section, and the temperature and humidity distribution characteristics of each layer are calculated step by step. S33, Mechanical response analysis: Based on the temperature and humidity changes of each fiber layer, the deformation and stress changes are calculated to obtain the overall stress distribution and curvature change of the cross section; S34, Results Output and Visualization: Outputs curves of stress, temperature and humidity changes and prestress loss at key sections of the beam, as well as stress and damage distribution diagrams of the sections.

[0012] Furthermore, the test-analysis co-calibration system in step S4 includes: The testing module includes the stress testing device and the data storage device; The analysis module has a built-in multi-field coupled fiber beam analysis program, which is used to receive the measured temperature and humidity data of the test module as environmental boundary conditions and update the thermal and humidity field and initial stress state of the fiber unit. The dynamic correction and visualization feedback module is used to achieve a one-to-one correspondence between test points and calculation fibers and to compare data, automatically correct model parameters and feed them back to the analysis module, and output structural performance evaluation results.

[0013] Furthermore, the preset threshold in step S4 is 5%. When the deviation between the measured stress and the calculated stress exceeds this threshold, the parameters corrected by the program include the concrete creep coefficient, humidity diffusion coefficient, thermal expansion coefficient, and damage evolution coefficient.

[0014] Furthermore, in step S1, the temperature and humidity sensor is an SHT45 humidity sensor with a measurement accuracy of temperature ±0.1℃ (5~60℃) and humidity ±1%RH (20~70%RH, @25℃); the strain gauge is a vibrating wire strain gauge, and the data is read by a multi-channel automatic frequency acquisition instrument; the acquisition instrument is a high-precision guide rail type weighing transmitter with a sampling frequency of 500Hz, a resolution of 1 / 500000, and a nonlinearity of 0.005%FS.

[0015] Furthermore, the soft gasket ring and the soft gasket are thin sheets of foam material formed by stamping, the rigid sleeve is a cylinder made of 304 stainless steel, the column-type tensile and compressive sensor is made of 40CrMo steel, the soft porous tube is a double-layer structure, and the size of each component can be adjusted proportionally according to the size of the structure and the size of the concrete aggregate.

[0016] Compared with existing technologies, the stress testing method for prestressed concrete beams under wet-heat-mechanical coupling proposed in this application has the following advantages: This application designs a stress testing device by rationally constructing a test zone, non-test zone, isolation zone, and rigid zone. Utilizing the principle of coordinated deformation between the test and non-test zones, the stress measured in the test zone is the actual stress, effectively eliminating the influence of strain unrelated to the test stress. The rigid zone of the testing device consists of a rigid sleeve and column-type tension / compression sensors, with stiffness far exceeding that of concrete of the same size, effectively avoiding interference from its own deformation on the measurement results. The isolation zone effectively separates the test and non-test zones through a soft porous tube, ensuring clear stress boundaries. This design effectively eliminates the influence of time-varying deformations such as concrete hardening, autogenous shrinkage, drying shrinkage, intrinsic creep, drying creep, thermal deformation, and thermal transition creep, which are unrelated to the test stress, enabling direct measurement of the true internal stress of the concrete. Compared to traditional strain methods that require indirect stress calculation through strain and complex corrections for irrelevant deformation components such as thermal expansion, hygroscopic expansion, and creep, this method requires no additional correction steps. It not only has higher testing accuracy but also stronger stability. It can be embedded in complex structures to achieve long-term service monitoring without interfering with the overall performance of the structure, providing a reliable basis of measured data for subsequent stress analysis.

[0017] This application deeply integrates the theories of moisture diffusion, heat transfer, micro-prestressed consolidation (MPS), and concrete damage constitutive model. Based on Timoshenko beam theory, it constructs a fiber beam calculation framework and establishes a multi-field coupled fiber beam analysis program, Bridge_analysis, encompassing humidity, heat, force, and damage. This program pre-integrates a cross-sectional humidity analysis module, a cross-sectional temperature analysis module, and a structural field analysis module. Each module is solved sequentially or semi-coupledly according to time steps. The temperature and humidity fields are solved first and mapped to the fiber elements. The structural field analysis module receives the parameters output by the temperature and humidity field modules and then calculates the cross-sectional stress, curvature, and overall beam response. The program comprises several modules: a cross-sectional humidity analysis module based on transient humidity diffusion control equations, considering the influence of temperature on the humidity diffusion coefficient; a cross-sectional temperature analysis module based on transient heat conduction control equations, calculating the temperature gradient distribution of each fiber layer through spatial discretization and time integration; and a structural field analysis module employing micro-prestressed consolidation (MPS) theory, Timoshenko beam theory, and beam element fiberization method. This enables efficient simulation of concrete shrinkage and creep, prestressed tendon stress relaxation, and time-varying internal force redistribution, significantly reducing the computational burden of complex three-dimensional detailed analysis. By dividing the beam cross-section into several fiber layers and calculating the temperature and humidity distribution characteristics of each layer step-by-step, the program can precisely reconstruct the temperature and humidity gradient changes from the surface to the core of the cross-section. This comprehensively reflects the stress evolution law of prestressed concrete beams in non-uniform environments, accurately assesses the comprehensive impact of temperature and humidity gradients, creep, and material damage on structural performance, and deeply reveals the stress evolution mechanism.

[0018] This application achieves closed-loop feedback between data and the model through a collaborative system consisting of a testing module, an analysis module, and a dynamic correction and visualization feedback module. The testing module deploys testing devices, temperature and humidity sensors, and strain gauges at key sections of prestressed concrete beams to collect stress, temperature, humidity, and strain data in real time and store them in a specific format. The analysis module has a built-in humidity-heat-mechanical coupling analysis program that automatically imports the temperature and humidity data collected by the testing module as environmental boundary conditions, updates the thermal and humidity field and initial stress state of the fiber units, and then completes stress calculation. The dynamic correction and visualization feedback module establishes a one-to-one correspondence between test points and calculated fibers, compares the measured stress with the calculated stress in real time, and automatically calls the parameter inversion module when the deviation exceeds a preset threshold to correct key parameters such as concrete creep coefficient, humidity diffusion coefficient, thermal expansion coefficient, and damage evolution coefficient, feeding the corrected parameters back to the analysis module for subsequent calculations. Simultaneously, the analysis results can be used to optimize the test point locations and data acquisition cycle, making the testing scheme more targeted. This collaborative system breaks through the limitations of traditional independent stress testing and structural analysis, and realizes dynamic evaluation of the stress state, environmental changes and performance degradation of concrete structures throughout the entire process, providing a solid scientific basis for long-term safety monitoring and life prediction of complex structures. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the stress testing device in the embodiments of this application; Figure 2 This is a schematic diagram illustrating the calculation and stratification of the temperature and humidity field in an embodiment of this application; Figure 3 This is a schematic diagram of the mechanical response analysis curve in an embodiment of this application; Figure 4 This is a visualized mid-span section stress diagram output from the embodiments of this application; Figure 5 This is a schematic diagram of the test-analysis collaborative system in the embodiments of this application; Figure 6 This is a schematic diagram of the uniaxial force test results in the embodiments of this application; Figure 7 This is a schematic diagram of temperature data testing, analysis, and fitting in an embodiment of this application; Figure 8 This is a schematic diagram of the temperature stress test and analysis results in the embodiments of this application; Figure 9 This is a schematic diagram showing the sensor deployment locations and different environmental conditions in the embodiments of this application; Figure 10This is a schematic diagram of the stress test and analysis results of a prestressed concrete beam under wet-heat-force coupling in an embodiment of this application.

[0020] Explanation of reference numerals in the attached figures: 1. Soft gasket; 2. Rigid sleeve; 3. Soft gasket; 4. Soft porous tube; 5. Positioning rod; 6. Column-type tension and compression sensor. Detailed Implementation

[0021] To make the technical solution and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0023] Furthermore, it should be noted that in the description of this application, if terms such as "upper," "lower," "inner," or "outer" appear, indicating orientation or positional relationship, these are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, if terms such as "first" or "second" appear, they are also used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] Furthermore, in the description of this application, unless otherwise expressly defined, the terms "installation," "connection," "joining," and "connector" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application in light of the specific circumstances.

[0025] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0026] The present application will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0027] In existing technologies, common methods for stress testing mainly include stress relief and strain measurement. Stress relief measures residual stress through local unloading, while strain measurement indirectly calculates stress using sensors such as resistance strain gauges, vibrating wire strain gauges, and fiber optic grating sensors. In addition, specialized sensors such as hydraulic flat plate stress sensors, specific types of concrete stress gauges, and intelligent embedded piezoelectric ceramic sensors have been developed for stress testing. In stress analysis, traditional analysis is mostly based on empirical models. In recent years, with the development of numerical methods, various coupled models have emerged, such as thermo-chemical-mechanical models, hydrothermal-mechanical coupled models, and micro-prestressed consolidation theory. Structural analysis often uses traditional beam theory, solid finite element methods, or fiber beam element models. Regarding test-analysis collaboration, with the development of structural health monitoring and digital twin concepts, related research attempts to combine measured multi-source monitoring data with physical coupled models, finite element analysis, and parameter inversion algorithms. Some pilot projects are also promoting the use of experimental monitoring data for model identification and online calibration.

[0028] Existing technologies have several shortcomings. In stress testing, current methods cannot effectively separate mechanical strain from temperature and humidity deformation strain. Differences in sensor characteristics, size, and concrete material properties, as well as stiffness mismatches, can lead to test results deviating significantly from the true stress values. In stress analysis, existing beam-and-trunk element models fail to adequately consider the coupling relationships between temperature, moisture migration, and material damage, making it difficult to accurately reflect long-term stress evolution patterns and resulting in poor performance evaluation under complex environments. Three-dimensional solid-state fine-grained stress analysis models require extensive computation, making them difficult to apply to large and complex structures. Regarding the collaboration between testing and analysis, there is a lack of effective coordination mechanisms. The interface between measured data and analysis models is inconsistent, making it difficult to effectively use test results for model correction and verification, thus affecting the reliability and accuracy of structural performance evaluation.

[0029] In view of this, in order to overcome the shortcomings of the existing technology, the stress testing method for prestressed concrete beams under wet-heat-mechanical coupling proposed in this embodiment refers to... Figures 1 to 5 This includes the following steps: S1, Deployment of stress testing device, temperature and humidity sensor and strain gauge: An embedded concrete stress testing device based on the principle of plane section coordination is deployed at the key section of the prestressed concrete beam, and temperature and humidity sensor and strain gauge are deployed at the same time.

[0030] In this step, the first step is to deploy the stress testing device sensors and strain gauges. The key sections of the prestressed concrete beam are areas where stress changes are more significant. By deploying embedded concrete stress testing devices based on the principle of plane section compatibility at these locations, internal stress information can be directly obtained. At the same time, with the addition of temperature and humidity sensors and strain gauges, relevant environmental and structural response data affecting the stress state can be comprehensively collected.

[0031] S2, Data Acquisition: After the concrete curing is completed, stress, temperature, humidity and strain data are collected in real time, and stress, temperature, humidity and strain-time curves are output.

[0032] In this step, after the concrete curing is completed, the data acquisition stage begins. At this time, the concrete structure has stable basic properties. Real-time acquisition of stress, temperature, humidity and strain data and output of stress-time curves can completely record the stress evolution characteristics of the structure in the early stage of service, providing real measured data support for subsequent analysis.

[0033] S3, Running the multi-field coupled fiber beam analysis program: The Bridge_analysis multi-field coupled fiber beam analysis program is developed based on MATLAB, Python or C++. The data collected in step S2, as well as the geometric parameters and material parameters of the beam, are input into the multi-field coupled fiber beam analysis program. The beam section is divided into several fiber layers, and the temperature and humidity distribution and mechanical response of each fiber layer are calculated step by step to obtain the results such as the stress distribution, curvature change and prestress loss of the section.

[0034] In this step, a multi-field coupled fiber beam analysis program based on humidity, heat, and force is run. This program is developed using a common programming environment and has good compatibility and scalability. The collected measured data, along with the beam's geometric and material parameters, are input into the program. The program divides the beam cross-section into several fiber layers and calculates the temperature and humidity distribution and mechanical response of each fiber layer step-by-step. This allows for a precise reconstruction of key indicators such as cross-sectional stress distribution, curvature changes, and prestress loss, solving the problem of traditional analysis methods' difficulty in accurately simulating multi-field coupling effects.

[0035] S4, Test-Analysis Collaborative Correction: Import the measured stress data into the multi-field coupled fiber beam analysis program, establish a one-to-one correspondence between test points and calculated fibers, and automatically call the parameter inversion module when the deviation between the measured stress and the calculated stress exceeds the preset threshold to correct the concrete creep coefficient, humidity diffusion coefficient, thermal expansion coefficient and damage evolution parameters, realize the dynamic calibration of the model of the multi-field coupled fiber beam analysis program, and output stress evolution curve, cross-sectional stress cloud diagram and structural performance evaluation results.

[0036] In this step, a test-analysis co-calibration is performed. After importing the measured stress data into the multi-field coupled fiber beam analysis program, a one-to-one correspondence is established between the test points and the calculated fibers, allowing direct comparison between the measured data and the calculation results. When the deviation between the two exceeds a preset threshold, the parameter inversion module is automatically invoked to correct the relevant parameters, achieving dynamic calibration of the model. The final output stress evolution curve, cross-sectional stress cloud map, and structural performance evaluation results provide a comprehensive and accurate basis for structural safety assessment.

[0037] Step S1 comprises three sub-steps, including S11, machining, calibration, and assembly. First, the components used to assemble the stress testing device are machined to ensure dimensional accuracy and assembly compatibility. The column-type tension / compression sensor is then installed into a rigid sleeve and calibrated to ensure measurement accuracy and eliminate the influence of sensor error on test results. Other components are then sequentially secured with bolts to form a stable whole, ensuring the device will not loosen or shift during use.

[0038] S12, Installation and Pouring: Install the assembled stress testing device into the formwork or reinforcing cage, ensuring the device is in the preset testing position. Simultaneous pouring of concrete in both the testing and non-testing areas ensures synchronous hardening of the concrete in both areas, forming a coordinated prism. This ensures consistent deformation between the testing and non-testing areas, avoiding deformation differences caused by asynchronous pouring. Stress values ​​are calculated by reading the test values ​​from the tension and compression sensors, enabling direct stress acquisition.

[0039] S13. Deployment and Calibration: Based on actual monitoring needs, stress testing devices and strain gauges are deployed at key locations such as the mid-span support area and tensioning end of the prestressed concrete beam. These areas are the core stress-bearing regions of the beam, enabling comprehensive capture of stress-strain changes. Humidity sensors are embedded at the upper and lower edges of the sealed and dry specimen sections to specifically measure humidity changes under different environmental conditions, providing data for analyzing the impact of humidity on stress. After deployment, zero-point calibration and sensitivity calibration are performed on all channels to ensure the consistency of signal output from each sensor and avoid data deviations caused by differences in sensor performance.

[0040] In step S13, the temperature and humidity sensor is an SHT45 humidity sensor with a measurement accuracy of temperature ±0.1℃ (5~60℃) and humidity ±1%RH (20~70%RH, @25℃); the strain gauge is a vibrating wire strain gauge, and the data is read by a multi-channel automatic frequency acquisition instrument; the acquisition instrument is a high-precision guide rail type weighing transmitter with a sampling frequency of 500Hz, a resolution of 1 / 500000, and a nonlinearity of 0.005%FS.

[0041] The temperature and humidity sensors used are of a specific model, possessing high measurement accuracy and capable of precisely capturing subtle changes in temperature and humidity. Temperature and humidity are crucial environmental factors affecting concrete performance and stress state; accurate temperature and humidity data provide reliable environmental parameter support for subsequent coupled analysis, avoiding deviations in analysis results due to environmental data errors. Vibrating wire strain gauges are employed; this type of strain gauge exhibits good stability and anti-interference capabilities, making it suitable for long-term strain monitoring of concrete structures.

[0042] Data acquisition via a multi-channel automatic frequency acquisition system enables simultaneous data acquisition from multiple strain measurement points, improving data acquisition efficiency while ensuring data consistency. Stress data acquisition utilizes a high-precision guide rail-type weighing transmitter, characterized by high sampling frequency, high resolution, and low nonlinearity. This allows for rapid and accurate acquisition of stress signals within concrete, capturing dynamic stress variations. These high-performance acquisition devices provide a high-quality foundation of measured data for the entire testing method, serving as a crucial element in ensuring accurate and reliable test results.

[0043] The multi-field coupled fiber beam analysis program in step S3 pre-integrates a cross-sectional humidity analysis module, a cross-sectional temperature analysis module, and a structural field analysis module. The cross-sectional humidity analysis module is based on the transient humidity diffusion control equation. Considering the influence of temperature on the moisture diffusion coefficient, the temperature factor is incorporated into the calculation process, enabling a more accurate calculation of the relative humidity distribution within the cross-section. Humidity, as a crucial factor affecting concrete shrinkage and creep, provides accurate distribution data for subsequent mechanical response analysis.

[0044] The cross-sectional temperature analysis module is based on the transient heat conduction control equation. By spatially discretizing and integrating the concrete cross-section over time, it can calculate the temperature gradient distribution of each fiber layer. The temperature gradient directly generates thermal stress and affects the material properties of concrete. The temperature gradient data output by this module is the main basis for thermal stress calculation and material property parameter correction.

[0045] The structural field analysis module employs the micro-prestressed consolidation MPS theory and the fiber-discrete Timoshenko beam theory. This combination of theories not only explains the creep mechanism at the microscopic level but also accurately simulates the macroscopic mechanical behavior of the beam. The module can calculate section stress curvature and overall beam response, and also simulate concrete shrinkage and creep, prestressing tendon stress relaxation, and time-varying internal force redistribution. It comprehensively considers the influence of various time-varying factors during the structure's service life, making the mechanical response analysis more closely reflect actual conditions.

[0046] The multi-field coupled fiber beam analysis program in step S3 employs multi-field coupled equations, among which the humidity field equation uses the Fick diffusion equation. This equation is a classic equation describing the diffusion process of matter and can effectively reflect the transmission law of humidity within concrete. Considering the change of boundary humidity gradient, it can accurately simulate the evolution of humidity distribution within concrete under different environmental humidity conditions, providing a mathematical basis for analyzing the influence of humidity on concrete performance and stress state.

[0047] The temperature field equation adopts the concrete heat transfer control equation, which conforms to the heat transfer characteristics of concrete materials and considers the influence of temperature changes on heat conduction. It can accurately calculate the temperature distribution and temperature gradient inside the concrete. Changes in the temperature field directly induce thermal strain and thermal stress, and simultaneously affect the mechanical properties and humidity diffusion coefficient of concrete. The application of this equation provides reliable temperature data support for thermo-mechanical and thermo-humidity coupled analysis.

[0048] The structural field equations are established based on the constitutive model of micro-prestressed consolidated MPS theory, combined with Timoshenko beam theory. MPS theory effectively describes the creep characteristics of concrete, considering the influence of temperature and humidity on creep; Timoshenko beam theory accurately simulates the bending and shear deformation of beams, and is particularly suitable for beam structural analysis under complex stress states. The structural field equations established by combining these two theories can comprehensively reflect the stress evolution of concrete beams under the combined action of temperature and humidity changes and mechanical loads, achieving deep coupling analysis of the moisture, heat, and mechanical fields.

[0049] Step S3 comprises four sub-steps, including S31, Input and Initialization, which involves inputting the collected measured data and the beam's geometric and material parameters into the multi-field coupled fiber beam analysis program. This provides comprehensive foundational data for the program's calculations. This data covers both the structure's inherent characteristics and the effects of the external environment, ensuring that the computational model accurately reflects the stresses and environmental conditions of the actual structure.

[0050] S32, Temperature and Humidity Field Calculation and Fiber Division, divides the beam cross-section into several fiber layers, enabling refined cross-sectional analysis. (Refer to...) Figure 2 By calculating the temperature and humidity distribution characteristics of each layer step by step, the temperature and humidity gradient changes from the surface to the core area of ​​the cross section can be accurately captured. This refined temperature and humidity data can provide accurate environmental parameter support for the subsequent mechanical response analysis of each fiber layer.

[0051] S33, Mechanical Response Analysis, Reference Figure 3By calculating deformation and stress changes based on the temperature and humidity variations of each fiber layer, the stress differences in concrete in different regions can be reflected. Simultaneously considering the relaxation effect of prestressing tendons and the influence of concrete creep and shrinkage, the stress evolution process of the structure under multiple factors can be comprehensively reconstructed. The overall stress distribution and curvature changes of the cross-section obtained through calculation can accurately reflect the mechanical state of the beam.

[0052] S34, the results output and visualization steps, transform complex calculation data into intuitive curves and charts. The output curves for key beam sections' stress, temperature and humidity changes, and prestress loss, as well as stress and damage distribution diagrams, clearly present the structure's stress state and performance evolution trends, facilitating structural performance evaluation and experimental comparison by technicians. (Refer to...) Figure 4 It is a visual stress diagram of the mid-span section, which can intuitively show the stress distribution state of the mid-span section.

[0053] Reference Figure 5 The test-analysis collaborative calibration system in step S4 consists of a testing module, an analysis module, and a dynamic calibration and visualization feedback module. These three modules form a closed-loop collaborative mechanism to ensure deep integration of testing and analysis. The testing module includes a stress testing device and a data storage device. The stress testing device is responsible for collecting key data such as stress, temperature, and humidity in real time, while the data storage device properly stores the collected data, forming a complete measured database. This module is the data source for the collaborative system, and the quality of the data it collects directly affects the effectiveness of subsequent analysis and calibration.

[0054] The analysis module incorporates a multi-field coupled fiber beam analysis program, receiving measured temperature and humidity data from the testing module as environmental boundary conditions to accurately recreate the environmental conditions during testing. Based on these boundary conditions, the analysis module updates the thermal and humidity field and initial stress state of the fiber elements, ensuring the calculation model remains consistent with the actual structural stress environment and providing accurate initial conditions for subsequent stress calculations.

[0055] The dynamic correction and visualization feedback module is the core hub of the collaborative system. It establishes a one-to-one correspondence between test points and computational fibers, enabling direct comparison between measured data and calculation results. After identifying deviations through data comparison, it automatically corrects model parameters and feeds them back to the analysis module, achieving dynamic optimization of the model. Simultaneously, this module outputs structural performance evaluation results, providing the final basis for structural safety assessment and ensuring the accuracy and reliability of the analysis results.

[0056] In step S4, a preset threshold of 5% is set as the standard for judging the accuracy of the model. When the deviation between the measured stress and the calculated stress exceeds this threshold, it indicates that there is a deviation between the parameter settings of the model and the actual situation, and parameter correction is required.

[0057] The corrected parameters include the concrete creep coefficient, humidity diffusion coefficient, thermal expansion coefficient, and damage evolution coefficient, all of which are key factors affecting concrete stress calculation. The concrete creep coefficient directly determines the magnitude of creep deformation, thus affecting long-term stress evolution; the humidity diffusion coefficient affects the humidity distribution inside the concrete, indirectly affecting shrinkage deformation and stress state; the thermal expansion coefficient determines the magnitude of thermal strain caused by temperature changes and is a core parameter for thermal stress calculation; the damage evolution coefficient reflects the degree of damage to the concrete material, and the development of damage will change the mechanical properties of the material, thus affecting stress distribution.

[0058] By automatically correcting these key parameters, the analysis model can continuously approximate the characteristics of the actual structure, gradually reduce the deviation between measured and calculated values, achieve adaptive optimization of the model, ensure the accuracy of subsequent calculation results, and provide reliable theoretical support for structural performance evaluation.

[0059] Reference Figure 1 The stress testing device in this embodiment comprises a rigid sleeve 1, a columnar tension / compression sensor 2, a soft gasket 3, a soft porous tube 4, a soft washer ring 5, and a positioning rod 6. These components work together to achieve accurate stress measurement. The rigid sleeve 1 serves as the basic support component of the device, providing a mounting carrier for other components. The columnar tension / compression sensor 2 is embedded inside the rigid sleeve 1, and together they form a rigid zone. The rigid zone has a stiffness more than eight times that of the concrete in the same area, effectively avoiding interference from its own deformation on the measurement results. This allows for direct measurement of the internal stress of the concrete, eliminating the need for indirect calculation through strain and reducing errors in intermediate steps. The soft gasket 3 is fitted to the bottom of the rigid sleeve, and the soft washer ring 5 is fitted to the top of the rigid sleeve. Both are soft in texture, allowing adjustment of the contact position between the rigid zone and the concrete, ensuring a tight fit between the rigid zone and the concrete and avoiding additional constraint stress, thus guaranteeing accurate stress transmission. A flexible porous tube 4 is inserted along the axial direction into the top of the rigid sleeve and connected to the column-type tensile and compressive sensor 2. It forms an isolation zone, effectively separating the concrete in the test area from the concrete in the non-test area, making the stress boundary of the test area clearer and preventing the deformation of the concrete in the non-test area from interfering with the test results. A positioning rod 6 is inserted perpendicularly to the axial direction into the side of the rigid sleeve 1. During device installation, the positioning rod 6 firmly secures the device in a preset position within the reinforcing cage or formwork, preventing displacement of the device during concrete pouring and ensuring the accuracy of the measurement position.

[0060] The soft gasket ring 5 and soft gasket 3 are made of thin foam sheets formed by stamping. The foam material has good softness and elasticity, forming a buffer between the rigid area and the concrete, avoiding additional stress caused by rigid contact. The stamping process ensures the dimensional accuracy of the components and guarantees a good fit after installation. The rigid sleeve 1 uses a stainless steel cylinder. Stainless steel has high strength and good stability, ensuring that the rigid sleeve will not deform during use, providing a stable installation environment for the column-type tension / compression sensor 2, and ensuring that the overall rigidity of the rigid area meets design requirements. The column-type tension / compression sensor 2 is made of 40CrMo steel, which has high strength, high toughness, and good mechanical stability. It can accurately sense stress changes and convert them into measurable signals, while also having a long service life, suitable for long-term stress monitoring. The soft porous tube 4 adopts a double-layer structure. The double-layer structure enhances the structural stability of the tube body, and the porous nature does not hinder the transmission of temperature and humidity, ensuring that the test area and non-test area are in a consistent temperature and humidity environment. This ensures that the isolation zone only serves a separating function and does not affect the consistency of environmental parameters.

[0061] The following section will demonstrate the effectiveness of the proposed method for testing the stress of prestressed concrete beams under wet-heat-force coupling through practical experiments.

[0062] First, concrete prism specimens measuring 15cm × 15cm × 40cm were prepared. The concrete strength grade was C50, the mixing ratio was 1:1.7:2.6 (cement:sand:aggregate), and the water-cement ratio was 0.38. The specimens were mixed using a forced mixer, compacted in layers, and cured in a standard curing room (20±2℃, relative humidity ≥95%) for 28 days before being used for testing.

[0063] Then, a stress testing device was set up on the axis of the specimen. The stress testing device was fixed inside the template, and the sensor axis was ensured to coincide with the loading direction. Concrete was poured according to the design mix ratio and compacted by vibration. After curing, the specimen was placed in an electronic universal testing machine, and multiple uniaxial compressions were performed with a loading rate controlled at 0.2 kN / s. Simultaneously, internal concrete pressure data, concrete strain data, and external load data were collected for comparative analysis.

[0064] Finally, the results are verified, referring to... Figure 6 The error between the internal stress measured by the stress testing device and the applied external compressive stress does not exceed 3%, and the curves match well, indicating that the device can accurately measure the internal stress of concrete under uniaxial stress.

[0065] Based on the above experiments, stress tests were conducted under complex temperature variation conditions, and the results were verified by coupling with numerical analysis.

[0066] First, the elastic modulus was tested. The elastic modulus of concrete was obtained based on uniaxial compression tests and taken as 30.43 GPa.

[0067] Next, the coefficient of thermal expansion was tested. Silicone heating plates were attached to all four sides of the specimen, and the temperature was precisely controlled (40±0.1℃) using a digital temperature controller. Three sets of tests were conducted with a temperature increase sequence from 20 to 40℃. The thermocouple temperatures (Ta, Tb, Tc) and the displacement of the top dial gauge were recorded. The average coefficient of linear expansion was calculated to be 7.83×10⁻⁶. -6 / K.

[0068] Next, temperature gradient stress testing was conducted. The temperature gradient stress test was set up with four heating conditions as shown in the table below, and the specimen was allowed to cool naturally under sealed conditions. The internal temperature was read by thermocouples, and the stress was recorded in real time by pressure sensors.

[0069]

[0070] Then, a multi-field coupled fiber beam analysis program was developed based on MATLAB, and parameters and boundary conditions were selected. Specifically, in the temperature boundary, the outer surface temperature was set according to the actual design conditions, ranging from 35℃ to 45℃; in the humidity boundary, the relative humidity was kept stable at 45%; and in the material parameters, based on the test results of the elastic modulus and thermal expansion coefficient of concrete, the elastic modulus and thermal expansion coefficient of concrete were set to 30.43 GPa and 7.83 × 10⁻⁶ GPa, respectively. -6 / K. Temperature test - analysis data fitting: thermal conductivity coefficient set to 1.5W / (m). K), specific heat is set at 0.95 kJ / (kg). K), refer to Figure 7 This indicates that, under the thermal parameters shown in the table above, the numerically calculated temperature field is highly consistent with the measured temperature curve.

[0071] Finally, numerical analysis and model verification are performed. The elastic modulus, coefficient of thermal expansion, thermal conductivity, and specific heat are input into the numerical analysis to calculate the temperature stress under four working conditions, and the results are compared with the measured internal stress. (Refer to...) Figure 8 The high degree of fit between the two models indicates that the model can accurately reflect the evolution of internal stress in concrete under different temperature gradients.

[0072] Based on the above experiments, stress tests were conducted on prestressed concrete beams under wet-heat-force coupling.

[0073] First, refer to Figure 9Stress testing devices (C1~C8) and strain gauges (B1~B4) were installed in the mid-span, support, and tensioning ends of the prestressed concrete beams according to actual needs. To monitor stress differences caused by temperature gradients, humidity sensors (H1~H3) were embedded at the upper and lower edges of the sealed and dry specimen sections to measure humidity changes under different drying and sealing conditions. After deployment, zero-point calibration and sensitivity calibration were performed on all channels to ensure signal output consistency.

[0074] Then, after the concrete pouring is completed and set, the test beams and specimens are demolded. Double layers of plastic are then adhered to the surfaces of the test beams and specimens to create a sealed environment and prevent moisture loss. (Refer to...) Figure 9 On day 49, the plastic film on the top plate of the test beam was removed, and the plastic films on the top and bottom of the humidity specimen were also removed to create dry conditions. During this period, the stress, strain of the beam, and humidity of the humidity specimen were recorded. On day 79, the plastic film on the web of the test beam was removed, and the stress, strain, and humidity of the beam and humidity of the humidity specimen were recorded during this period.

[0075] All sensor signals are recorded in real time through a synchronous acquisition system. The system has a built-in time calibration and phase correction module to achieve synchronous acquisition and unified time base for humidity, temperature, and stress signals. Environmental parameters (temperature and humidity time histories) also serve as external field input boundaries, providing realistic boundary conditions for subsequent numerical calculations.

[0076] Then, a multi-field coupled model of humidity, heat, and force was established based on the Bridge_analysis program developed using MATLAB. The beam cross-section and span dimensions, as well as concrete and steel reinforcement material information, were input according to the actual test results of the PC beam. The measured temperature and humidity time-history data were used as the model boundary inputs. Parameter selection and boundary conditions included: temperature boundary (outer surface temperature based on actual monitoring results); humidity boundary (relative humidity based on actual monitoring conditions); and load boundary (considering self-weight, prestress, and vehicle loads).

[0077] Finally, refer to Figure 10 The system can plot synchronous curves of measured and calculated results, and output a distribution cloud map of cross-sectional stress at a specific moment. This result intuitively reflects the influence of temperature and humidity changes on prestress transfer and time-varying behavior of concrete, and can be used to predict the long-term evolution trend of gradient stress within a structure.

[0078] The above descriptions are merely some embodiments of this application and are not intended to limit this application. The technical features or structures in the foregoing different embodiments can be arbitrarily combined to form other specific technical solutions as needed. For those skilled in the art, this application can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of the claims of this application.

Claims

1. A method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling, characterized in that, Includes the following steps: S1, Deployment of stress testing device, temperature and humidity sensor and strain gauge: Deploy embedded concrete stress testing device based on the principle of plane section coordination at key sections of prestressed concrete beam, and deploy temperature and humidity sensor and strain gauge at the same time. S2, Data Acquisition: After the concrete curing is completed, stress, temperature, humidity and strain data are collected in real time, and stress, temperature, humidity and strain-time curves are output. S3, Run the wet-thermal-mechanical coupled fiber beam analysis program: Compile a multi-field coupled fiber beam analysis program based on MATLAB, Python or C++, input the data collected in step S2 and the geometric parameters and material parameters of the beam into the multi-field coupled fiber beam analysis program, divide the beam section into several fiber layers, calculate the temperature and humidity distribution and mechanical response of each fiber layer step by step, and obtain the results such as cross-sectional stress distribution, curvature change and prestress loss; S4, Test-Analysis Collaborative Correction: Import the measured stress data into the multi-field coupled fiber beam analysis program, establish a one-to-one correspondence between test points and calculated fibers, and automatically call the parameter inversion module when the deviation between the measured stress and the calculated stress exceeds the preset threshold to correct the concrete creep coefficient, humidity diffusion coefficient, thermal expansion coefficient and damage evolution parameters, realize the dynamic calibration of the model of the multi-field coupled fiber beam analysis program, and output stress evolution curve, cross-sectional stress cloud diagram and structural performance evaluation results.

2. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 1, characterized in that, The stress testing device includes: Rigid sleeve (1); A column-type tensile and compressive stress sensor (2) is embedded inside the rigid sleeve (1) to form a rigid zone with the rigid sleeve (1) for deformation coordination and to realize direct measurement of internal stress in concrete. A soft pad (3) is fitted to the bottom of the rigid sleeve (1) to adjust the contact position between the rigid sleeve (1) and the concrete. A soft porous tube (4) is inserted into the top of the rigid sleeve (1) along the axial direction and connected to the column-type tensile and compressive sensor (2) to form an isolation zone to separate the concrete in the test area from the concrete in the non-test area. A soft pad ring (5) is fitted to the top of the rigid sleeve (1) and is used to adjust the contact position between the rigid sleeve (1) and the concrete in conjunction with the soft pad (3). The positioning rod (6) is inserted perpendicularly to the side of the rigid sleeve (1) and is used to limit the position inside the steel cage or formwork.

3. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 2, characterized in that, Step S1 includes the following sub-steps: S11, process each component of the stress testing device, install the column-type tensile and compressive sensor (2) into the rigid sleeve (1) and calibrate it, and then fix other components in sequence with bolts; S12, the stress testing device is installed into the template or steel cage, and then concrete is poured simultaneously in the test area and the non-test area. After hardening, a coordinated prism is formed, and the stress value is calculated by reading the test values ​​of the tension and compression sensors. S13, The stress testing device and strain gauge are respectively arranged in the mid-span area, support area and tensioning end of the prestressed concrete beam according to actual needs; After deployment, zero-point calibration and sensitivity calibration were performed on all channels to ensure signal output consistency. Humidity sensors were embedded at the upper and lower edges of the cross-section to measure humidity changes under different drying and sealing conditions. Under the same environment, sealed specimens and specimens with different drying conditions were made for the calibration of concrete material performance parameters.

4. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 1, characterized in that, The multi-field coupled fiber beam analysis program in step S3 is pre-integrated with multiple functional modules, including: The cross-sectional humidity analysis module is based on the transient humidity diffusion control equation, taking into account the influence of temperature on the humidity diffusion coefficient, and calculates the relative humidity within the cross section. The cross-sectional temperature analysis module is based on the transient heat conduction control equation and calculates the temperature gradient distribution of each fiber layer through spatial discretization and time integration. The structural field analysis module uses the micro-prestressed consolidation MPS theory and the fiber-discrete Timoshenko beam theory to calculate the section stress, curvature and overall beam response. It also simulates concrete shrinkage and creep, steel reinforcement constraint, prestressing tendon stress relaxation and time-varying internal force redistribution.

5. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 1, characterized in that, The multi-field coupling equations used in the multi-field coupled fiber beam analysis program in step S3 include: The humidity field equation adopts the Fick diffusion equation, taking into account the change of boundary humidity gradient; The temperature field equation adopts the concrete heat transfer control equation, taking into account the influence of temperature changes on heat conduction. The structural field equations are established based on the constitutive model of micro-prestressed consolidation MPS theory, combined with Timoshenko beam theory and beam element fiberization analysis method.

6. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 1, characterized in that, Step S3 includes the following sub-steps: S31, Input and Initialization: Input the data collected in step S2, as well as the beam's geometric parameters and material parameters, into the multi-field coupled fiber beam analysis program. S32, Temperature and humidity field calculation and fiber division: The beam section is divided into several fiber layers according to the temperature and humidity distribution law of the section, and the temperature and humidity distribution characteristics of each layer are calculated step by step. S33, Mechanical response analysis: Based on the temperature and humidity changes of each fiber layer, the deformation and stress changes are calculated to obtain the overall stress distribution and curvature change of the cross section; S34, Results Output and Visualization: Outputs curves of stress, temperature and humidity changes and prestress loss at key sections of the beam, as well as stress and damage distribution diagrams of the sections.

7. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 1, characterized in that, The test-analysis collaborative calibration system in step S4 includes: The testing module includes the stress testing device and the data storage device; The analysis module has a built-in multi-field coupled fiber beam analysis program, which is used to receive the measured temperature and humidity data of the test module as environmental boundary conditions and update the thermal and humidity field and initial stress state of the fiber unit. The dynamic correction and visualization feedback module is used to achieve a one-to-one correspondence between test points and calculation fibers and to compare data, automatically correct model parameters and feed them back to the analysis module, and output structural performance evaluation results.

8. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 7, characterized in that, The preset threshold in step S4 is 5%. When the deviation between the measured stress and the calculated stress exceeds this threshold, the parameters corrected by the program include the concrete creep coefficient, humidity diffusion coefficient, thermal expansion coefficient, and damage evolution coefficient.

9. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 1, characterized in that, In step S1, the temperature and humidity sensor is an SHT45 humidity sensor with a measurement accuracy of temperature ±0.1℃ (5~60℃) and humidity ±1%RH (20~70%RH, @25℃); the strain gauge is a vibrating wire strain gauge, and the data is read by a multi-channel automatic frequency acquisition instrument; the acquisition instrument is a high-precision guide rail type weighing transmitter with a sampling frequency of 500Hz, a resolution of 1 / 500000, and a nonlinearity of 0.005%FS.

10. The method for testing the stress of prestressed concrete beams under wet-heat-mechanical coupling according to claim 2, characterized in that, The soft pad ring (5) and the soft pad (3) are foam sheets formed by stamping. The rigid sleeve (1) is a 304 stainless steel cylinder. The column-type tensile and compressive sensor (2) is made of 40CrMo steel. The soft porous tube (4) is a double-layer structure. The dimensions of each component can be adjusted proportionally according to the structural dimensions and the concrete aggregate dimensions.

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